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Full text of "Rapid Population Growth Consequences And Policy Implications"

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together of large numbers of susceptible young men with a few infected individuals. But there is evidence that crowding also has other injurious health effects, which occur primarily during the period when the degree and extent of crowding is rapidly increasing. The effects appear to be much less serious when the rate of crowding is slow and the crowded population has sufficient time to become adapted to its environment.
Thus rapid population growth and its accompanying rapid urbanization are probably more injurious to health than actual population density. In many cases, however, it is difficult to isolate the effects of crowding, as such, from other conditions, such as poverty, poor nutrition, poor housing, and pollution, which formerly characterized all cities and still prevail in the rapidly growing cities of the poor countries, and in the "inner cities" of the United States.
Before the modern era, cities were often called "eaters of men"—their birth rates were usually lower than their death rates, and the population was maintained by continuing migration from the countryside. Even as late as 1950, urban death rates in the United States were slightly higher than rural ones. But by 1960 the situation had reversed, and in 1966 death rates in cities and towns were only half as high as those in rural areas. The incidence of infectious illness was much lower. This was at least partly the result of better sanitation and health facilities in the cities and suburban towns, relative to the rural areas, plus the fact that migration of younger people to the cities had left an older, more susceptible population behind in the countryside. Low morbidity and mortality also characterize crowded areas in other countries with high levels of health services and sanitation. For example, although Hong Kong and Holland have very high population densities, they are said to enjoy two of the highest levels of physical and mental health in the world. The levels of mortality and morbidity in the densely populated cities and towns of Great Britain are about the same as those in rural areas.
Both animal experiments and experience with human beings indicate that social stresses due to crowding produce physiological disturbances. In turn, these increase susceptibility to both infectious and noninfectious disease. The effects are most severe before individuals have had time to become adapted to the crowded conditions. In animals, physiological changes occur during the period when the size of the population in the same space, that is, the population density, is increasing. These changes include increased adrenal and other endocrine secretions and a higher level of activation of the central nervous system. It is believed that they result from increased social interactions which enhance emotional involvement and produce excessive sensory stimuli. Animals in subordinate positions within the group tend to respond in a far more extreme fashion than those at the top of the social hierarchy, both in the volume of endocrine secretions and in manifestations of disease and pathol-osv. After the nooulation has reached its maximum size and has become